Preparation of crystalline hot melt composition

ABSTRACT

Thermoplastic adhesive polycarbonamide-ester compositions having molecular weights ranging from about 2000 to 7000, a viscosity of about 2000 to 5000 centipoise at 160°C. and a tensile shear strength of about 75 to 140 pounds per 1 inch × 1/2 inch lap, which are useful in the formation of creep resistant adhesive bonds in product assembly between laminae of relatively impervious materials such as glass, metals and certain of the plastics, e.g. polyethylene. An outstanding product assembly of this invention is a container of composite construction having a glass envelope of thin walled construction in the shape of an inverted light bulb bonded to a plastic cup-like base member with the above described thermoplastic adhesive composition.

This is a division of application Ser. No. 336,769, filed Feb. 28, 1973,now abandoned, which application was a division of application Ser. No.156,693 filed June 25, 1971, now U.S. Pat. No. 3,749,630.

BACKGROUND OF THE INVENTION

This invention relates to polycarbonamide-ester compositions, methods offorming creep resistant bonds between impervious materials andcontainers of composite construction. More particularly, this inventionrelates to containers of composite construction formed from a glassenvelope of thin wall construction adhesively bonded with a hot meltadhesive, that is the product of the condensation of a dicarboxylic acidand an alkanolamine or a mixture of alkanolamine and diamine, to aplastic (preferably polyethylene) cup-like base designed for engagingthe bottom or major portion of the glass envelope.

Ever since the introduction of the first commercial ethylenevinylacetate copolymers in the early 1960's, there has been an everincreasing demand for thermoplastic resins as adhesives by thepackaging, and more recently by the product assembly industries. Of theseveral unique benefits hot melts have to offer over conventionalbonding methods -- gap filling, speed, ability to bond impervioussurfaces, reduced machinery cleanup time -- speed is the onecharacteristic most often emphasized, since this property alone canoften make the difference between a successful and unsuccessfulpackaging line.

With the increasing shift in application of thermoplastic adhesives fromthe packaging to the product assembly industries, has come a shift inthe emphasis with respect to the critical properties of thermoplasticadhesives. The tolerances for product assembly hot-melts are very muchmore critical than those for adhesives used in packaging where ratherwide variations in application techniques, temperature, and otherprocessing conditions can usually be tolerated without a great deal ofdifficulty.

The greater demands placed on thermoplastic adhesives by the productassembly industry has resulted in the development of a whole new classof so-called "high performance adhesives" based on polyesters,hydroxyvinyl resins, and polyamide polymers and copolymers. These morerecently developed high performance thermoplastic adhesives, in additionto a number of the properties previously listed for conventionalthermoplastic packaging adhesives, generally have increased tensilestrength, greater flexibility, greater degree of wettability on a largernumber of substrates, increased creep resistance, increased resistanceto environmental conditions and sharper melting points.

Separate articles by J. R. Harrison and J. C. Hunt appearing in theOctober 1969 and August 1970 issues of "Adhesive Age" respectively,provide a relatively complete summary of the problems encountered in theuse and selection of product assembly hot-melts and some of theadvantages and limitations of specific adhesives currently in commercialuse.

My invention is the discovery of certain relatively low molecular weightpolycarbonamide-ester compositions which form highly creep resistantadhesive bonds between laminae generally acknowledged to be imperviousto such materials. The strength of the adhesive bond is believed to be afunction of the crystallinity of the adhesives which gradually increaseswith the aging of the adhesive. This unusually high degree of creepresistance of the adhesive when cured, coupled with the highly favorableflow characteristics of the polymer compositions at temperatures in therange of from about 125° to 175°C. make my adhesives very highlyfavorable as a product assembly hot melt.

SUMMARY OF THE INVENTION

My invention is a creep resistant thermoplastic adhesive composition,having a tensile shear strength of about 75 to 140 pounds per 1 inch ×1/2 inch lap, an average molecular weight of about 2,000 to 7,000 and aviscosity of about 2,000 to 5,000 cps at 160°C., which is the product ofthe condensation of a stoichiometric amount of a saturated aliphaticdicarboxylic acid having a hydrocarbon chain length of 4 to 12 carbonatoms, with a stoichiometric amount of a saturated alkanolamine having ahydrocarbon chain length of 2 to 6 carbon atoms.

In the preferred embodiment of my invention, the creep resistantthermoplastic adhesive composition is prepared by the condensation of astoichiometric amount to 7.0 mole percent excess of a saturatedaliphatic dicarboxylic acid having a hydrocarbon chain length of 4 to 10carbon atoms, with a stoichiometric amount of a mixture comprising 70.0to 99.0 mole percent, based on dicarboxylic acid, of a saturatedaliphatic alkanolamine having a hydrocarbon chain length of 2 to 6carbon atoms and 1.0 to 30.0 mole percent, based on dicarboxylic acid,of a saturated aliphatic diamine having a hydrocarbon chain length of 2to 6 carbon atoms, or a symmetrical alicyclic diamine having ahydrocarbon ring of 8 carbon atoms.

Additional embodiments of my invention include a method for formingcreep resistant adhesive bonds between laminae of relatively imperviousmaterials and the articles of composite construction prepared thereby.

DESCRIPTION OF THE DRAWING

FIG. 1 is a perspective view and partial section of a container ofcomposite construction prepared according to the method of thisinvention.

FIG. 2 is a cross-sectional view through a laminate also preparedaccording to the method of this invention.

In FIG. 1, a glass envelope 2 is adhesively bonded along its entirecircumference at a common adhesive interface 4 to the upstandingcylindrical wall portion of a cup-like fitment 3 by a thin continuousannular band 1 of thermoplastic adhesive along a common adhesiveinterface.

In FIG. 2, two juxtaposed laminae 15 and 16 of relatively imperviousmaterials are bonded to one another in sandwich-like fashion by aninterlayer of creep resistant thermoplastic adhesive 17 at theirrespective adhesive interfaces 14.

DESCRIPTION OF THE INVENTION INCLUDING PREFERRED EMBODIMENTSThermoplastic Adhesives

1. Monomeric Components -- The thermoplastic adhesives of this inventionare polycarbonamide-ester copolymers prepared by the condensationpolymerization of a dicarboxylic acid with an alkanolamine or with amixture of an alkanolamine and a diamine.

The dicarboxylic acid monomers which can be used in the preparation ofthe thermoplastic adhesives of this invention have the followingstructural formula: ##EQU1## wherein,

R is a saturated aliphatic hydrocarbon radical of 4 to 10 carbon atoms.

Representative of the dicarboxylic acid monomers which can be used inthe preparation of the thermoplastic adhesive compositions of thisinvention are hexanedioic acid (adipic acid), heptane-dioic acid(pimelic acid), octanedioic acid (suberic acid), nonanedioic acid(azelaic acid) and decanedioic acid (sebacic acid).

The preferred dicarboxylic acid monomers of this invention are adipic,azelaic and sebacic acid.

All of the dicarboxylic acid monomers used in the preparation of thepolycarbonomide-ester adhesives of this invention are either readilyavailable as reagent grade chemicals or can be prepared by standardlaboratory synthesis.

Alkanolamine monomers of the polycarbonamide-ester adhesives of thisinvention can be represented by the following structural formula,##EQU2## wherein,

R' is a saturated aliphatic hydrocarbon radical of 2 to 6 carbon atoms,including ethyl, propyl, pentyl and hexyl.

Alkanolamines representative of the alkanolamine monomers which can beused in the preparation of the polycarbonamide-ester adhesivecompositions of this invention are ethanolamine, 3-amino-1-propanol, and6-amino-1-hexanol.

The preferred alkanolamine monomers of this invention have hydrocarbonchain lengths in the range of from 2 to 4 carbon atoms, withethanolamine being the most preferred of this group.

Most, if not all, of the alkanolamine monomers of this invention arereadily available as reagent grade chemicals and where not so availablecan be prepared by simple standard laboratory techniques.

The diamine monomers of the polycarbonamide-ester adhesive compositionsof this invention can be represented by the following structuralformula, ##EQU3## wherein,

R" is a saturated aliphatic hydrocarbon radical of 2 to 6 carbon atomsor a symmetrical alicyclic hydrocarbon radical of 8 carbon atoms, namelyethylene and hexamethylene.

Typical of the diamine monomers which can be used in thepolycarbonamide-ester adhesive compositions of this invention areethylene diamine and 1,6 hexamethylene diamine, with ethylene diaminebeing most preferred.

The same holds true as to the commercial availability of the diaminemonomers as indicated for the other monomer components of the adhesivecompositions of this invention. Those diamines not readily available asstock reagents can be prepared by standard synthesis techniques.

2. Adhesive Preparation -- The polycarbonamide-ester adhesivecompositions of this invention can be prepared by standard meltpolymerization techniques from monomer mixtures comprising astoichiometric amount of a saturated aliphatic dicarboxylic acid havinga hydrocarbon chain length of 4 to 12 carbon atoms and a stoichiometricamount of a saturated alkanolamine having a hydrocarbon chain length of2 to 6 carbon atoms. The preferred polycarbonamide-ester adhesivecompositions of this invention are those having a more favorablecombination of viscosity and tensile sheer strength, and can be preparedby standard melt polymerization techniques from stoichiometric amountsto 7.0 mole percent excess of a saturated aliphatic dicarboxylic acidhaving a hydrocarbon chain length of 4 to 12 carbon atoms with astoichiometric amount of a mixture comprising 70.0 to 99.0 mole percentbased on dicarboxylic acid, of a saturated aliphatic alkanolamine havinga hydrocarbon chain length of 2 to 6 carbon atoms, and 1.0 to 30.0 molepercent based on dicarboxylic acid, of a saturated aliphatic diaminehaving a hydrocarbon chain length of 6 carbon atoms, or a symmetricalalicyclic diamine having a hydrocarbon ring of 8 carbon atoms.

For a comprehensive description of the apparatus and techniquesgenerally employed in the melt polymerization process, reference can bemade to any of the standard texts on polymer preparation e.g. Sorensonand Campbell, "Preparative Methods of Polymer Chemistry", IntersciencePublishers, Inc., New York (1961).

The adhesive compositions of this invention can be prepared by charginga reaction vessel equipped with a thermometer, a nitrogen gas inlet anda distilling condenser with the monomers of either of the two systemsdisclosed above. The reaction vessel is first purged with nitrogen, themonomers melted, and then heated at refluxing temperatures for a periodof at least 15 minutes, but usually not more than 3 hours. Ordinarily,the reaction temperatures will vary with changes in pressure on thesystem; refluxing of the monomers at reduced pressures taking place atlower temperatures and the reverse occurring at higher pressures.Preferably, the reaction temperature of the system should be maintainedat about 200°C. at one atmosphere to control the degree ofpolymerization which in turn limits the molecular weight of thecopolymers. After the condensation of monomer has proceededsubstantially to completion, the reaction vessel is turned todistillation and the temperature gradually increased over a period of 3hours to about 235°C. Simultaneous with this change-over todistillation, the pressure on the charge is also reduced to about 5 to10mm of Hg. The polymer is collected and either used directly whilestill fluid or allowed to cool and harden. The polymer thus produced istransparent while fluid; however, it becomes milky and opaque when bulkset. If the copolymer is uniformly smeared in a thin film between twolaminae, e.g. a glass slide and a polyethylene tab, the copolymeradhesive also becomes increasingly opaque upon setting and aging,indicative of the gradual growth of crystals within the copolymer.

METHOD FOR BONDING IMPERVIOUS LAMINAE Impervious Laminae

The laminae which are to be bonded by thermoplastic adhesives accordingto the methods of this invention are component parts or layers of anadhesively bonded sandwich or any element which is to be bonded to aseparate element in the manufacture of an article of compositeconstruction. Such laminae are composed of impervious materials whichare generally recognized to be relatively impenetrable by, ornonabsorbent, of fluid media, such as the thermoplastic adhesives ofthis invention. Impervious materials which can be bonded to themselvesor dissimilar materials by thermoplastic adhesives of this invention areglass, polyethylene, polyvinyl chloride, and various metals such asiron, aluminum, copper and their alloys. An alloy of one of the abovemetals comprises in excess of 50 weight percent of one of thespecifically enumerated metals together with minor amounts of one ormore additional metal forming components. A typical alloy of one of theenumerated metals which can be bonded by my thermoplastic adhesivesaccording to the method of this invention is stainless steel.

The preferred laminae of this invention are glass and low to highdensity polyethylene.

The glass composition of the glass laminae of this invention does notappear to be of critical importance, and any of the glass compositionscurrently in use in the manufacture of such articles as light bulbs,beverage containers, television tube envelopes and auto glass shouldprove amenable to bonding with the adhesive of this invention.Similarly, the polyethylene composition of the polyethylene laminae ofthis invention doesn't appear critical; provided that, such compositiondoes not contain additives, such as antioxidants, flame retardants,etc., in amounts which prove functionally significant with respect tothe adherence of the adhesive to the polyethylene laminae.

The laminae of the articles of composite construction of this inventioncan take any form and therefore can be bonded to one another in avariety of ways depending, of course, upon the intended structure of theultimate assemblage.

Laminae typical of those which can be bonded by the adhesives of thisinvention are the component parts of the structures disclosed in U.S.Pat. No. 3,482,724 (to R. A. Heaton). The glass envelopes disclosedtherein are thin wall structures terminating in an open mouth at oneend, an intermediate concavely curved neck region 8 and a lower or majorportion 9 of the envelope which is constructed with an outlineapproximating that of a major section sphere 9a. This lower or majorportion of the envelope is of a substantially circular configuration inhorizontal section at every elevation of such portion and substantiallycontinuously convexly arcuate in all axial sections, (vertical planespassing through the central vertical axis of the envelope), of theenvelope. The second element of Heaton's container, a cup-like fitment3, can be designed for engaging the lower or major portion of the glassenvelope at an interface coincident with the exterior lateral wall ofthe envelope and the interior of the upstanding cylindrical wall of thefitment. The cup-like fitment can also engage the envelope at the nadirof arc of the spherical wall of the envelope which itself can bespecially adapted for such engagement by slightly flattening the arc ofthe container at that point. The above mentioned patent of Heaton ishereby incorporated by way of reference into the disclosure of thisapplication.

METHOD OF BONDING

Articles of manufacture can be prepared from two or more laminae ofrelatively impervious materials utilizing the thermoplastic adhesivecompositions of this invention by bonding these laminae along theircommon points of engagement to one another with such adhesives. Themanner of application of the adhesive, the amount of adhesive requiredto effectively join such laminae and the strength of the bond thusproduced will vary from composite to composite depending upon thephysical nature of the materials to be bonded and the stresses to beendured at the point of engagement by the components of the proposedcomposite.

The thermoplastic adhesives of this invention can ordinarily be appliedto either one or both components of the composite to be assembled. Thetechnique for applying such materials can vary, from the rather slowconventional manual methods of applying such adhesives, to the highspeed, automated dispensing systems commonly employed in the packagingand product assembly industries. The amount of adhesive applied to thecomponents is also variable depending upon the physical surfacecharacteristics of the respective laminae and the mechanicalconfiguration of the adhesive junction. For example, the amount ofadhesive required to join smooth surfaces will be considerably greaterthan the amount required to effectively bond an abraded surface.Similarly, the amount of adhesive required to effectively withstand thestresses encountered by a butt joint wil substantially exceed thatnecessary to effectively bond a dove tail-type junction. This point ofadhesive application can be generally described as an adhesive interfacewhich is defined in terms of that area on each component part (orlamina) which is in contact with or separated from a coincident orabutting adhesive interface of a juxtaposed lamina by a deposit or thinlayer of adhesive. Areas falling within this definition include alsosurfaces which are designated as the situs for the deposition ofadhesive or designated to be contacted by a surface of a lamina havingsuch adhesive deposits.

Once the melt of the adhesive has been applied to one or more of thecomponent parts of a composite article, the respective elements of sucharticle can be aligned and seated, while the adhesive is still fluid.Alternatively, the adhesive can be allowed to set for a sufficientinterval after the application until it forms a self-supporting film.Setting can be expedited by subjecting the adhesive to a chilling blastof cool air or carbon dioxide. Once having set, the adhesive can beremelted, either by exposing it to temperatures in excess of itsvisco-elastic temperature range or by contacting the adhesive with asurface of a second lamina that is heated sufficiently to cause theadhesive to flow.

After the adhesive interfaces of the component parts (or laminae) of theproposed article to be assembled are coated with adhesive wherenecessary, the parts can be aligned and seated along their intendedpoints of engagement. Once so assembled, the original registration ofthe component parts as seated must be maintained at least until suchtime as the adhesive has sufficiently cured or aged to withstand theinitial stresses which may be placed upon the adhesive bond by theweight of the respective elements of the composites themselves. Goodinitial bond strength can be accelerated in the same manner utilized inthe expediting of the setting of adhesive discussed previously. However,the curing or aging of the adhesive, more specifically, the gradualincrease in the degree of crystallinity of the thermoplastic adhesivecomposition of this invention is developed only with passing time. Inmany instances, once the composite has been assembled, as in the case ofthe composite container depicted in FIG. 1, the intimate or interlockingunion of the components or the force of gravity, as in the case of thelaminate depicted in FIG. 2, are often sufficient in and of themselvesto retain the original alignment of the component parts.

The interval required to cure or age the adhesive, and thus develop therequisite creep resistance necessary in the adhesive to resistelongation under stress, usually takes at least 1 to 24 hours, dependingupon the particular adhesive composition.

Preparation of composite articles of manufacture utilizing the adhesivecompositions of this invention can also involve the assembly of morethan two component parts at a single time by merely distributing theadhesive along the several adhesive interfaces of the parts to beassembled, followed by aligning and seating the component parts asdesired. This method of assembly can be used in the preparation ofmultiple layered laminates or in other related applications.

It is also possible to prepare a multiple layer laminate by merelyrecycling the composite of a previous cycle with additional laminae.

The following examples further illustrate the adhesive compositions,methods and composite articles of manufacture of this invention. Partsand percentages wherein appearing in such examples are by weight unlessotherwise stipulated.

EXAMPLE I

A three neck 250 ml flask, fitted with a thermometer, N₂ gas inlet and adistilling condenser, is charged with 75.2 gm (0.4 moles) azelaic acidand 24.4 gms (0.4 moles) of ethanolamine. The mixture is refluxed fortwo hours under a nitrogen blanket at a pot temperature of 140°C. and arefluxing temperature of 98°C. The system is now turned to distillation,gradually increasing the pot temperature of the system to 200°C. over aperiod of one hour. At the end of the third hour, the pressure on thesystem is reduced to about 10 mm Hg and pot temperature again graduallyincreased over the next 3 hours to 230°C. The polymer is collected in analuminum pan, cooled to 160°C. and its viscosity recorded at 2860 cps.

After the copolymer product has cooled to about 160°C. it is manuallyapplied in a uniform continuous annular band to the interior upstandingcylindrical wall of a cup-like fitment. The copolymer is then set with achilling blast of carbon dioxide. Once the copolymer has set, the openend of the cup-like fitment is brought into alignment with the convexlyarcuate portion of the major segment of a glass envelope which is stillsufficiently residually heated from its forming operation to cause theadhesive to flow upon contact. Once the two elements are aligned,preferably with the vertical axis of the envelope at right angles to thehorizontal base of the fitment, they are seated. The container thusproduced is stored in an inverted position overnight in order to insuresufficient curing of the adhesive so that registration is maintainedbetween the two elements. This container demonstrates good resistance tovertical creep when subject to loads equal to and in excess of thatanticipated to be encountered in use.

EXAMPLE II

Following the procedure of Example I, a copolymer having a viscosity of1750 cps at 160°C. is prepared from equimolar amounts of azelaic acidand 3-amino-1-propanol. The copolymer formed is capable of forming creepresistant adhesive bonds between glass and low to medium densitypolyetylene, as well as a variety of other impervious laminae.

EXAMPLE III

Following the procedure of Example 1, a copolymer having a viscosity of1900 cps at 160°C. is prepared from equimolar amounts of sebacic acidand 3-amino-1-propanol. The copolymer formed is capable of forming creepresistant adhesive bonds between glass and low to medium densitypolyethylene, as well as a variety of other impervious laminae.

EXAMPLE IV

Following the procedure of Example I, a copolymer having a viscosity of4490 cps at 160°C. is prepared from equimolar amounts of adipic acid and3-amino-1-propanol. The copolymer formed is capable of forming creepresistant adhesive bonds between glass and low to medium densitypolyethylene, as well as a variety of other impervious laminae.

EXAMPLE V

Following the procedures of Example I, a copolymer having a viscosity of2320 cps at 160°C. is prepared from 1.06 moles adipic acid and 1.00moles of a mixture comprising 85.0 mole percent ethanolamine and 15.0mole percent 1,6 hexamethylenediamine. The copolymer formed is capableof forming creep resistant adhesive bonds between glass and low tomedium density polyethylene, as well as a variety of other imperviouslaminae.

EXAMPLE VI

Following the procedures of Example I, a copolymer having a viscosity of2040 cps at 160°C. is prepared from 1.06 moles azelaic acid and 1.00moles of a mixture comprising 85.0 mole percent ethanolamine and 15.0mole percent ethylenediamine. The copolymer formed is capable of formingcreep resistant adhesive bonds between glass and low to medium densitypolyethylene, as well as a variety of other impervious laminae.

EXAMPLE VII

Following the procedures of Example I, a copolymer having a viscosity pf2470 cps at 160°C. is prepared from stoichiometric amounts of 1.06 molesazelaic acid and 1.00 moles of a mixture comprising 85.0 mole percent3-amino-1 propanol and 15.0 mole percent ethylenediamine. The copolymerformed is capable of forming creep resistant adhesive bonds betweenglass and low to medium density polyethylene, as well as a variety ofother impervious laminae.

What I claim is:
 1. In a container of composite construction formed of aglass envelope having a mouth opening at one end thereof and beingsubstantially continuous convexly arcuate in the axial section along asubstantial extent of its end portion disposed opposite said mouth, anda cup-like polyethylene fitment bonded to said envelope by hot meltadhesive means the improvement wherein said adhesive means is an annularband of creep resistant thermoplastic adhesive having a tensile shearstrength of about 75 to 140 pounds per 1 inch × 1/2 inch lap, and anaverage molecular weight of about 2,000 to 7,000, said thermoplasticadhesive being the polymeric product of the condensation of a monomermixture consisting essentially of (a) a stoichiometric amount to about 7mole percent excess of a compound of the formula ##EQU4## wherein R is asaturated aliphatic hydrocarbon radical of 4-10 carbon atoms, and (b) acompound of the formula NH₂ --R'--OH wherein R' is a saturated aliphatichydrocarbon radical of 2 to 6 carbon atoms, or a mixture of 70 to 99mole percent of a compound of the formula NH₂ --R'--OH, wherein R' is asaturated aliphatic hydrocarbon radical of 2 to 6 carbon atoms with 1 to30 mole percent of a compound of the formula NH₂ --R"--NH₂ wherein R" isa saturated aliphatic hydrocarbon radical of 2 to 6 carbon atoms or asymmetrical alicyclic hydrocarbon radical of 8 carbon atoms.
 2. Theimprovement of claim 1, wherein said adhesive is the polymeric productof the condensation of a monomer mixture consisting essentially of saidcompound of the formula ##EQU5## and said mixture of a compound of theformula NH₂ --R' --OH with said compound of the formula NH₂ --R' --NH₂.3. The improvement of claim 1 wherein said adhesive is the polymericproduct of the condensation of a monomer mixture consisting essentiallyof said compound of the formula ##EQU6## and said compound of theformula NH₂ --R'--OH.
 4. The improvement of claim 1 wherein saidcompound of the formula ##EQU7## is a azelaic acid.
 5. The improvementof claim 1 wherein said compound of the formula ##EQU8## is adipic acid.6. The improvement of claim 1 wherein said compound of the formula##EQU9## is sebacic acid.
 7. The improvement of claim 1 wherein saidcompound of the formula NH₂ --R'--OH is ethanolamine.
 8. The improvementof claim 1 wherein said compound of the formula NH₂ --R'--OH is3-amino-1-propanol.